What turbo for 9:1 compression, GTX28/30?

[Manji]

Originally Posted by Reaper

I think its not worth buying another turbo when he can just put pistons in it and achieve his result at a lower psi and will make more usable torque.

The pistons aren't the problem. The rods are.

Clearly he just wants to buy a built block. One that comes in at 9.0:1 . What I am saying is that a 2L at that static comp using a gtx2867r is a great combination; because the motor running at that comp means the turbo will be boosting harder; and it's more efficient when boosting harder. So that comp and a gtx2867r end up being a great combo.

Run high static comp, the motor is more efficient. Because the motor is more efficient it means it's less of a restriction. Because it's less of a restriction it can ingest more air. This means to make the same power the turbo is operating at a lower boost level. This isn't necessarily a good thing.

Look at any modern turbo and note where the choke line is at given pressure ratios. Where the choke line extends it's furtherst to the right should be the target pressure ratio. This means that running lower static comp so that the turbo is operating at its ideal pressure ratio will result in optimum power.

That's why people running a gtx28 at 7psi will say the turbo will choke in the top end. Look where the choke line and therefore the efficentcy zones at that pressure ratio on the comp map and you'll see why. Now if they ran lower static comp, then the turbo can operate at a more ideal pressure ratio; and the setup will make more power with the same turbo.

[Manji]

Also, your comment about lower static comp will result in more usable torque is incorrect. Because he is knock governed by pump fuel.

Lowering the static comp would allow him to ramp up a small turbo very aggressively. Something you can't do at 12.5:1 on pump fuel.

[Synack]

Thanks for all of the replies guys. Lots of good info here. @Manji do you believe I can achieve 400whp with the GTX2867R on my compression efficiently?

Originally Posted by Manji

Clearly he just wants to buy a built block. One that comes in at 9.0:1 .

I've already got the 9:1 compression

[Manji]

Originally Posted by Synack

Thanks for all of the replies guys. Lots of good info here. @Manji do you believe I can achieve 400whp with the GTX2867R on my compression efficiently?



I've already got the 9:1 compression

Yes easily. You'll get there at 1.0 - 1.1bar, assuming it can rev. I have a very similar setup myself.

If its a stock head it'll probably need 1.2 bar.

Either way, 1.0 - 1.2 bar are ideal operating pressures for a gtx2867r. That where the efficency islands are at their widest.

[Synack]

Originally Posted by Manji

Yes easily. You'll get there at 1.0 - 1.1bar, assuming it can rev. I have a very similar setup myself.

That's about 15psi, are you serious? That's crazy.

[Manji]

I'll also add that one thing I have noticed about forums is there seems to be this obsession with "High comp low boost for the win"

Probably because one person said it once, and the rest are just jumping on the bandwagon.

In the real world, with real world limitations like pump fuel, you'll find the opposite is true.

I'm not saying that high comp is bad. I'm saying too many people are looking at their turbo builds through NA-knowledge-tinted sunglasses.

Lets take a practical example. Using this motor and a gtx2867r (yes I love this turbo)
On 7psi making 300whp at 12.5:1, that pretty much all your going to get. Knock limited. Which in part is caused by the turbo operating at this level inefficeintly, but mostly because of the static comp. (This is why a bigger turbo at this level achieves marginally more power, as it's landing in a better efficency zone at that point.
But if you run the same motor at LOWER static comp, meaning the gtx28 has to BOOST harder (that doesn't mean is working harder, work should be judged by effiency zones) it will make 400whp at 14psi and end up at the same efficency zone. (So IMO similar work load on the turbo) You also wont be governed by knock as you could spike the mid range up higher if you wanted to.

A 2 litre motor, running a gtx28 frame turbo at 400whp, at 9.0:1 static comp will NOT have poor throttle response.

[Manji]

Originally Posted by Synack

That's about 15psi, are you serious? That's crazy.

Because you're no longer near the knock threshold, you can get more aggressive with the tune, which is where a lot of throttle response really comes from.

You can't get that aggressive on pump fuel & 300whp & 12.5:1 c/r.

[Synack]

Originally Posted by Manji

I'll also add that one thing I have noticed about forums is there seems to be this obsession with "High comp low boost for the win"

Probably because one person said it once, and the rest are just jumping on the bandwagon.

In the real world, with real world limitations like pump fuel, you'll find the opposite is true.

I'm not saying that high comp is bad. I'm saying too many people are looking at their turbo builds through NA-knowledge-tinted sunglasses.

Lets take a practical example. Using this motor and a gtx2867r (yes I love this turbo)
On 7psi making 300whp at 12.5:1, that pretty much all your going to get. Knock limited. Which in part is caused by the turbo operating at this level inefficeintly, but mostly because of the static comp. (This is why a bigger turbo at this level achieves marginally more power, as it's landing in a better efficency zone at that point.
But if you run the same motor at LOWER static comp, meaning the gtx28 has to BOOST harder (that doesn't mean is working harder, work should be judged by effiency zones) it will make 400whp at 14psi and end up at the same efficency zone. (So IMO similar work load on the turbo) You also wont be governed by knock as you could spike the mid range up higher if you wanted to.

A 2 litre motor, running a gtx28 frame turbo at 400whp, at 9.0:1 static comp will NOT have poor throttle response.

Fantastic, thanks man.

Originally Posted by Manji

Because you're no longer near the knock threshold, you can get more aggressive with the tune, which is where a lot of throttle response really comes from.

You can't get that aggressive on pump fuel & 300whp & 12.5:1 c/r.

I'll have to ask my tuner to get more aggressive because I'm at 350whp at 20psi right now on my Precision 5431.

[Manji]

Originally Posted by Synack

Fantastic, thanks man.

I'll have to ask my tuner to get more aggressive because I'm at 350whp at 20psi right now on my Precision 5431.

I'd recommend swapping the cams out. That's whats holding you back.

I can't really divulge too much about it.

But its the head causing the restriction that is governing that boost level.

NA cams are often not very good FI cams.

I'm not familar with precision turbos at all, but even a tiny gtx2860r will hit 350whp at 20psi. But I'm point to the head, not the turbo.

[Synack]

Originally Posted by Manji

I'd recommend swapping the cams out. That's whats holding you back.

I can't really divulge too much about it.

But its the head causing the restriction that is governing that boost level.

NA cams are often not very good FI cams.

I'm not familar with precision turbos at all, but even a tiny gtx2860r will hit 350whp at 20psi. But I'm point to the head, not the turbo.

Well I'll see what we can get from the current setup with a retune, just with an added water line because the GTX is oil/water, and v-band.

If I'm not getting close to 400whp then I'll cam it out.

Edit: I take that back. Cams are barely out, if at all, for this car. Not to mention they wouldn't be cheap since we need 4. And you have to pull the motor to install. Sounds like a ~$3000 job to me.

[Dipstik-sportech]

Pte5858 and I've hit higher than that on lesser quality fuel

[Manji]

You don't have to pull the motor to put cams in.

All the main camshaft manufacturers are putting their efforts into developing FI cams at the moment; due to the disappointed results from NA cams.

Early next year there will be some good options coming to market.

[Synack]

Originally Posted by Dipstik-sportech

Pte5858 and I've hit higher than that on lesser quality fuel

Honestly I'll probably never go back to Precision.

Were your results on 9:1 compression?

[D K]

Originally Posted by ciro

BW 7163

Mixed flow FTW